Process for the recovery of hydrogen/heavy hydrocarbons from hydrogen-lean feed gases

Abstract

The process of this invention is a hybrid gas separation process which recovers both heavy hydrocarbon and high purity hydrogen products from a gas stream containing a relatively low concentration of hydrogen. The heavy hydrocarbon product may consist of C 2 +, C 3 + and/or C 4 + hydrocarbons. The light hydrocarbons and other light components, such as N 2 and CO, are removed as a light fuel gas stream. After convertional removal of any components which might freeze at low temperatures, the feed gas is combined with recycle gas from the hydrogen purifier and fed to the cryogenic unit.

We claim: 
     
       1. In a process for the separation and recovery of heavy hydrocarbon and high purity hydrogen products from a feed gas stream containing heavier hydrocarbons and a relatively small concentration of hydrogen, wherein the gas stream is cleaned of acid gases and dehydrated; the cleaned, dehydrated feed gas stream is separated in a cryogenic separation system producing a light fuel gas stream, at least one heavy hydrocarbon product stream, and a hydrogen-enriched gas stream; and the hydrogen-enriched gas stream is purified in a hydrogen purifier thereby producing a high purity hydrogen product stream and a purifier reject stream which is recycled and combined with the cleaned, dehydrated feed gas stream as a combined feed to the cryogenic separation system; the improvement comprising: (a) cooling and partially condensing the combined feed;   (b) separating the cooled and partially condensed combined feed into a liquid and a vapor phase;   (c) cooling and partially condensing the vapor phase in a dephlegmator wherein in partially condensing the vapor phase, a rectified liquid condensate is recovered from the dephlegmator and warmed to recover refrigeration;   (d) further cooling and partially condensing the non-condensed portion of the vapor phase in indirect heat exchange thereby producing a hydrogen-enriched gas phase and a light fuel liquid phase;   (e) separating the hydrogen-enriched gas phase from the light fuel liquid phase;   (f) warming at least a portion of the liquid phase of step (b) to recover refrigeration;   (g) removing the warmed liquid phase of step (f) and the warmed rectified liquid condensate of step (c) as heavy hdrocarbon product;   (h) flashing and vaporizing the light fuel liquid phase of step (e) to recover refrigeration thereby producing a light fuel gas stream; and   (i) warming the hydrogen-enriched gas of step (e) to recover refrigeration and feeding the warmed, hydrogen-enriched gas to the hydrogen purifier.   
     
     
       2. The process of claim 1 which further comprises compressing the hydrogen-enriched gas prior to feeding to the hydrogen purifier. 
     
     
       3. The process of claim 1 which further comprises compressing the heavy hydrocarbon product. 
     
     
       4. The process of claim 1 wherein the hydrogen purifier is a membrane separation unit comprising at least one stage. 
     
     
       5. The process of claim 1 wherein the hydrogen purifier is a pressure swing adsorption unit. 
     
     
       6. The process of claim 1 which further comprises compressing the light fuel gas stream. 
     
     
       7. The process of claim 1 which further comprises compressing the purified hydrogen product from the hydrogen purifier. 
     
     
       8. The process of claim 1 which further comprises compressing the recycle gas stream from the hydrogen purifier. 
     
     
       9. The process of claim 1 wherein the feed gas stream contains less than 40 mole% hydrogen; the high purity hydrogen product stream contains more than 95 mole% hydrogen; and at least 90 vol% of the hydrogen in the feed gas stream is recovered in the high purity hydrogen product stream. 
     
     
       10. The process of claim 1 wherein the heavy hydrocarbon product is fed to a distillation column for further separation and purification. 
     
     
       11. The process of claim 1 wherein the hydrogen-enriched gas is work expanded to provide refrigeration prior to feeding the work expanded, warmed hydrogen-enriched gas to the hydrogen purifier.